Question: The scale on a map is 8cm : 5km. If two cities are 72cm apart on the map, what is the actual distance in km between the two cities?
The scale means that every 8cm on the map corresponds to an actual distance of 5km. A distance of 72cm on the map is the same as 9 $\cdot$ 8cm. The actual distance between the two cities is 9 $\cdot$ 5km, or 45km.